This patch disallows deleting / modifying system defined guest OS mappings

Local env
1. Create user defined mapping
2. Delete / modify user defined mapping. Should pass
3. Delete / modify system defined mapping. Should fail

Signed off by :- Nitin Mehta<nitin.mehta@citrix.com>
CLOUDSTACK-6652 CLONE - [Automation] Vmware-  System's StartCommand failed with "NumberFormatException" while using VMware DVS

vlan id format was like "vlan://<id>" instead of just "<id>". This causes numberformatexception while converting the vlan id to integer form from string form. this was fixed for standard vswitch in bug Cloudstack-5046. now fixed for other 2 cases of dvswitch as well as pvlan.

Signed-off-by: Sateesh Chodapuneedi <sateesh@apache.org>